At present, the power output of systems comprising a synchronous electrical machines as such, and an exciter which generates electric current to excite said machine, has increased dramatically to reach 1,200 to 1,300 megawatts. Systems with a power output of 1,600 to 2,000 megawatts are being developed. The increase in the power output is accompanied by an increase in exciting currents transmitted through the rotary part of the system from the exciter to the electrical machine. Transmission of such currents from the exciter to the electrical machine necessitates the use of highly reliable contact devices which can withstand increased vibration and centrifugal loads.
There is known a device to electrically connect the rotor winding of a synchronous electrical machine to an exciter comprising conductors, which are arranged in axial bores of the rotor shaft of the synchronous electrical machine and of the exciter shaft and are constructed as current-conducting rods, and flexible annular current-conducting washers that are insulated from the shaft. The current-conducting rods arranged in the axial bores of the rotor shaft of the synchronous electrical machine and the exciter shaft are connected to flexible buses, the place of connection being where said rods come out of said bores, said flexible buses being, in turn, bolted to said current-conducting washers.
This device is far too complicated. In addition, the flexible buses are not protected from the effects of centrifugal forces, which makes the device mechanically unreliable.
There is also known a device to electrically connect rotor leads of a synchronous electrical machine to an exciter, which comprises buses radially extending into the zone of conjugated half-sleeves and joined by bolts received in through holes of half-sleeves' flanges.
In this device, the electrically conjugated surfaces are located in the zone of the flanges of the half-sleeves, so the flange area, which is intended for torque transmission, is reduced; on the other hand, heavy exciting currents require large electrically conjugated surfaces, which accounts for a considerable increase in the flange size.
Besides, in this device the supply buses and the means to insulate them from the shaft are too complicated, because the heavy buses, which are bent at a right angle to the rotational axis of the machine, are subjected to substantial centrifugal loads caused by rotation of the shaft.
There is also known an electromechanical coupling unit which is used primarily in electrical machines. In this unit, the rotor windings are connected through wedge contacts.
This unit is marked by a large number of components; it is also complicated due to a large number of contacts.
Finally, there is known a contact device of a synchronous electrical machine, which is intended to electrically connect the rotor winding of the electrical machine to the latter's exciter.
The portions of the leads of the rotor winding of the synchronous electrical machine and of the exciter, which are to be connected, extend through the central bores of the shafts, are bent at a right angle and are tapered; arranged therebetween is a resilient current-conducting wedge provided with a longitudinal slot.
The device under review has two intermediate contacts for one polarity, whereby the reliability of the electrical connection is reduced. Furthermore, the manufacturing procedure envisages careful matching (for one polarity) of four conjugated tapered contact surfaces, which is a complicated task.
In addition, the assembly of this device requires a special device to hold in place the wedge at the moment the generator and exciter shafts come into contact.